This invention relates generally to sheet feeders and, more specifically, to a combination recirculating document feeder and document positioner.
It is known in the art to provide a copier with a document feeder that presents a set of document sheets seriatim to an exposure station of the copier to produce one or more collated sets of copies without the need for a collator. Such apparatus is disclosed in the commonly assigned U.S. Reissue Pat. No. Re. 27,976 and in the commonly assigned U.S. Pat. No. 4,169,674, which issued on Oct. 2, 1979 in the name of Matthew J. Russel and is entitled RECIRCULATING SHEET FEEDER. In the document feeder disclosed in U.S. Pat. No. 4,169,674, a set of document sheets are stacked in a tray and removed seriatim, beginning with the bottom sheet in the tray, by an oscillating vacuum feeder. A removed sheet is inverted once and fed to a platen where the document sheet is registered and exposed once to produce a copy of the sheet. Then the sheet is inverted a second time and returned to the stack of sheets in the tray on top of other sheets in the tray. This process continues until all the sheets in the set of document sheets have been copied one or more times. The copy sheets are fed, one after another, into a stack in a tray with the first copy sheet being at the bottom and other copy sheets being received seriatim on top of previously delivered copy sheets. The information copied faces upwardly on each copy sheet and the resulting copy sets are arranged in the same page sequence order as the set of document sheets. Similar recirculating feeder apparatus is described in commonly assigned U.S. Pat. Nos. 4,076,408 and 4,078,787.
It is also known to provide document feeder apparatus wherein either simplex or duplex document sheets can be fed to a platen for copying in a recirculating feeder and to provide, in combination therewith, a document positioner useful for feeding one or more document sheets to the platen for copying one or more times, and then removing such sheets from the platen along a nonrecirculating sheet path. Such apparatus is disclosed in the commonly assigned U.S. Pat. No. 4,176,945 which issued on Dec. 4, 1979 in the names of R. C. Holzhauser et al, and is entitled SHEET FEEDING APPARATUS FOR USE WITH COPIER/DUPLICATORS OR THE LIKE, and in a related publication appearing as item No. 17351 on pages 44-48 of Volume 173 (September 1978 Edition) of Research Disclosure, such being available from Industrial Opportunities, Ltd., Homewell, Avant, Hampshire, P.O. 9-1EF, United Kingdom.
It is known to use oscillating vacuum tubes or cylinders for feeding sheets of paper from a stack of sheets. For example, the paper feeder disclosed in Halahan et al U.S. Pat. No. 2,770,458 includes an oscillating vacuum cylinder having three coaxial sections located beneath a stack of sheets. A pair of bearings is located at the ends of the center section of the cylinder and drive belts are trained around the bearings. The bearings are located relative to the vacuum cylinder so that the belts are recessed below the surface of the cylinder sections directly beneath the stack of sheets but project above the surface of the cylinder sections at a point spaced about 60.degree. from the stack of sheets. The cylinder sections can remove a sheet from the stack and advance the sheet to a position where it contacts the drive belts. At that point, nip rollers urge the sheet against the drive belts for advancement by the belts.
In copier/duplicators it is common practice to register document sheets at a side or corner of a platen for exposure. Accordingly, document feeding apparatus of the type mentioned hereinbefore typically moves the document sheet across the platen toward such a registration edge or corner. A gate mechanism located at the registration position is engaged by the document sheet to locate the sheet in position for exposure. As disclosed in U.S. Pat. Nos. 4,076,408, 4,078,787 and 4,169,674, the document sheet continues to be driven against the gate mechanism after initial contact between the document sheet and the gate mechanism to correct any skew in the sheet. Also, sheet registration can be achieved by driving a sheet feeding roller mechanism a given number of revolutions to advance a document page across a copier platen to a registration edge at the far side of the platen. The latter type of registration is disclosed in the beforementioned Reissue Patent No. Re. 27,976.
The use of drive rollers to advance document sheets can cause the sheets to become skewed. Skewing is less pronounced when vacuum belts are used for advancing sheets. The use of vacuum belts for advancing sheets is disclosed in a number of publications, including item No. 15,056, which appears at pages 47 and 48 of the October, 1976 Edition of Research Disclosure, and in U.S. Pat. Nos. 3,984,099, 4,033,694, 4,043,669 and 4,047,812. In addition, U.S. Pat. No. 3,698,706 illustrates a vacuum belt system for photoconductive copy sheets wherein a sheet sensor is used to stop a drive to the belts and to simultaneously brake the belts, thereby to instantly stop the belts at the position required for projection of an image onto the desired portion of the copy sheet. Also, British Pat. No. 1,411,550 teaches the use of sheet sensors to stop a document sheet at a registration position for copying of the sheet.
In some cases it is desirable to invert a document or copy sheet. For example, a duplex document sheet has information on both sides that is to be copied. First one side of the document sheet is exposed for copying, then it is inverted and the second side of the sheet is exposed for copying. IBM Technical Disclosure Bulletin, Volume 14, No. 5, page 1547 discloses a sheet inverting apparatus wherein a sheet is driven around a roller to invert it. Other sheet inverting apparatus are disclosed in IBM Technical Disclosure Bulletin, Volume 19, No. 12, page 4496 and in U.S. Pat. Nos. 3,575,507, 4,052,128 and 4,066,252.
In some prior devices drive rollers used for advancing sheets may induce skewing of the sheets. Also the sheets may have to travel along relatively long paths leading to a registration position on a platen, and this increases the likelihood of sheets becoming skewed and increases the time required for delivery of a sheet to the registration position. Mechanical registration devices, such as bars or feet, frequently are used to register a sheet on the platen. Apparatus is required for moving these feet into and out of a position where they can register sheets, and sometimes images of these feet or bars are formed on copy sheets.